Classifications

• • C—CHEMISTRY; METALLURGY
  • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
  • C08K—Use of inorganic or non-macromolecular organic substances as compounding ingredients
  • C08K5/00—Use of organic ingredients
  • C08K5/0008—Organic ingredients according to more than one of the "one dot" groups of C08K5/01 - C08K5/59
  • C08K5/0025—Crosslinking or vulcanising agents; including accelerators
• • C—CHEMISTRY; METALLURGY
  • C07—ORGANIC CHEMISTRY
  • C07C—ACYCLIC OR CARBOCYCLIC COMPOUNDS
  • C07C45/00—Preparation of compounds having >C = O groups bound only to carbon or hydrogen atoms; Preparation of chelates of such compounds
  • C07C45/27—Preparation of compounds having >C = O groups bound only to carbon or hydrogen atoms; Preparation of chelates of such compounds by oxidation
  • C07C45/30—Preparation of compounds having >C = O groups bound only to carbon or hydrogen atoms; Preparation of chelates of such compounds by oxidation with halogen containing compounds, e.g. hypohalogenation
• • C—CHEMISTRY; METALLURGY
  • C07—ORGANIC CHEMISTRY
  • C07C—ACYCLIC OR CARBOCYCLIC COMPOUNDS
  • C07C45/00—Preparation of compounds having >C = O groups bound only to carbon or hydrogen atoms; Preparation of chelates of such compounds
  • C07C45/61—Preparation of compounds having >C = O groups bound only to carbon or hydrogen atoms; Preparation of chelates of such compounds by reactions not involving the formation of >C = O groups
  • C07C45/67—Preparation of compounds having >C = O groups bound only to carbon or hydrogen atoms; Preparation of chelates of such compounds by reactions not involving the formation of >C = O groups by isomerisation; by change of size of the carbon skeleton
  • C07C45/68—Preparation of compounds having >C = O groups bound only to carbon or hydrogen atoms; Preparation of chelates of such compounds by reactions not involving the formation of >C = O groups by isomerisation; by change of size of the carbon skeleton by increase in the number of carbon atoms
  • C07C45/70—Preparation of compounds having >C = O groups bound only to carbon or hydrogen atoms; Preparation of chelates of such compounds by reactions not involving the formation of >C = O groups by isomerisation; by change of size of the carbon skeleton by increase in the number of carbon atoms by reaction with functional groups containing oxygen only in singly bound form
  • C07C45/71—Preparation of compounds having >C = O groups bound only to carbon or hydrogen atoms; Preparation of chelates of such compounds by reactions not involving the formation of >C = O groups by isomerisation; by change of size of the carbon skeleton by increase in the number of carbon atoms by reaction with functional groups containing oxygen only in singly bound form being hydroxy groups
• • C—CHEMISTRY; METALLURGY
  • C07—ORGANIC CHEMISTRY
  • C07C—ACYCLIC OR CARBOCYCLIC COMPOUNDS
  • C07C49/00—Ketones; Ketenes; Dimeric ketenes; Ketonic chelates
  • C07C49/76—Ketones containing a keto group bound to a six-membered aromatic ring
  • C07C49/84—Ketones containing a keto group bound to a six-membered aromatic ring containing ether groups, groups, groups, or groups
• • C—CHEMISTRY; METALLURGY
  • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
  • C08F—MACROMOLECULAR COMPOUNDS OBTAINED BY REACTIONS ONLY INVOLVING CARBON-TO-CARBON UNSATURATED BONDS
  • C08F283/00—Macromolecular compounds obtained by polymerising monomers on to polymers provided for in subclass C08G
  • C08F283/01—Macromolecular compounds obtained by polymerising monomers on to polymers provided for in subclass C08G on to unsaturated polyesters

Definitions

• the invention relates to new benzil-monoacetals, to a new process for the production of benzil-monoacetals and to their use as sensitisers for photopolymerisation of polymerisable systems containing unsaturated compounds, as well as to their use for the photochemical cross-linking of polymerisates.
• unsaturated monomers or mixtures thereof with unsaturated polymers can be photochemically polymerised in the presence of suitable sensitisers such as carbonyl compounds containing a halogen in the ⁇ -position with respect to the carbonyl group, mercaptans, aromatic disulphides, nitroso compounds, azo compounds, benzoins and benzoin ethers.
• suitable sensitisers such as carbonyl compounds containing a halogen in the ⁇ -position with respect to the carbonyl group, mercaptans, aromatic disulphides, nitroso compounds, azo compounds, benzoins and benzoin ethers.
• R 1 represents hydrogen, alkyl having 1 to 5 carbon atoms, alkenyl having 2 or 3 carbon atoms, aralkyl having 7 to 9 carbon atoms, aralkenyl having 8 or 9 carbon atoms, or a group --(CH 2 ) n --X,
• X represents halogen, --OR 3 , --SR 3 , --OAr 3 , ##STR2##
• n represents a whole number from 1 to 3
• R 2 represents a group ##STR3##
• R 3 represents alkyl having 1 to 4 carbon atoms
• R 4 represents hydrogen or alkyl having 1 to 18 carbon atoms
• Ar 1 , Ar 2 and Ar 3 each independently represent a phenyl radical unsubstituted or at most trisubstituted by halogen, alkyl or --Oalkyl having 1 to 4 carbon atoms or by phenyl.
• R 1 represents hydrogen, alkyl having 1 to 3 carbon atoms, benzyl, ⁇ -styrene or a group --(CH 2 ) n --X,
• X represents chlorine, bromine, --OR 3 , --SR 3 , --OAr 3 or --SAr 3 ,
• n 1 or 2
• R 2 represents --(CH 2 ) 3 -- or --(CH 2 ) 2 --
• R 3 represents alkyl having 1 to 3 carbon atoms
• Ar 1 and Ar 2 each independently represent a phenyl radical unsubstituted or mono- or disubstituted by chlorine, bromine, alkyl or -Oalkyl having 1 to 3 carbon atoms, and
• Ar 3 represents phenyl
• R 1 represents hydrogen, alkyl having 1 to 3 carbon atoms or a group --CH 2 --X,
• X represents chlorine, bromine or --OCH 3 and
• Ar 1 and Ar 2 represent phenyl.
• R 1 represents alkyl having 1 to 5 carbon atoms, alkenyl having 2 or 3 carbon atoms, aralkyl having 7 to 9 carbon atoms, aralkenyl having 8 or 9 carbon atoms or a group --(CH 2 ) n --X,
• X represents halogen, --OR 3 , --SR 3 , --OAr 3 , --SAr 3 , ##STR4##
• n represents a whole number from 1 to 3
• R 2 represents a group ##STR5## or --(CH 2 ) 3 --
• R 3 represents alkyl having 1 to 4 carbon atoms
• R 4 represents alkyl having 1 to 18 carbon atoms
• Ar 1 , Ar 2 and Ar 3 each independently represent a phenyl radical unsubstituted, or at most trisubstituted by halogen, alkyl or -Oalkyl having 1 to 4 carbon atoms or phenyl,
• Ar 1 or Ar 2 or Ar 1 and Ar 2 represent a phenyl radical substituted as defined
• R 1 and R 4 can also represent halogen.
• Preferred compounds of formula I or Ia are compounds wherein
• R 1 represents alkyl having 1 to 3 carbon atoms, vinyl, benzyl, ⁇ -styrene or a group --(CH 2 ) n --X,
• X represents chlorine, bromine, --OR 3 , --SR 3 , --OAr 3 or SAr 3 ,
• n 1 or 2
• R 2 represents --(CH 2 ) 3 --
• R 3 represents alkyl having 1 to 3 carbon atoms
• Ar 1 and Ar 2 each independently represent a phenyl radical unsubstituted, or mono- or disubstituted by chlorine, bromine, alkyl or -Oalkyl having 1 to 3 carbon atoms, and
• Ar 3 represents phenyl
• Ar 1 or Ar 2 or Ar 1 and Ar 2 represent a phenyl radical substituted as defined
• R 1 can also represent hydrogen and R 2 also --CH 2 -CH 2 --;
• R 1 represents alkyl having 1 to 3 carbon atoms or a group --CH 2 --X
• X represents chlorine, bromine or --OCH 3 and
• Ar 1 and Ar 2 represent phenyl.
• R 1 , R 3 and R 4 of formula I denote alkyl radicals, then, within the given limits, these can be, for example, methyl, ethyl, propyl, isopropyl, butyl, sec.butyl, tert.butyl, amyl, hexyl, octyl, dodecyl, 2-ethylhexyl or octadecyl.
• R 1 can be an alkenyl radical such as vinyl, ⁇ -methylvinyl, propenyl or allyl.
• R 1 can be, e.g. benzyl, ⁇ -methylbenzyl, ⁇ , ⁇ -dimethylbenzyl, ⁇ -phenylethyl or ⁇ -phenylvinyl.
• Ar 1 , Ar 2 and Ar 3 as a substituted phenyl radical are: 4-chlorophenyl, 2-bromophenyl, 2,4-dichlorophenyl, 3-methylphenyl, 4-sec.butylphenyl, 2-chloro-4-ethylphenyl, 4-ethoxyphenyl, 2-methoxy-4-chlorophenyl, 2,4,6-trichlorophenyl or 3,5-dichloro-4-propoxyphenyl.
• Examples of compounds of formula I are: benzil-diethylacetal, benzil-dipropylacetal, benzil-dibutylacetal, benzil-di( ⁇ -phenylethyl)acetal, benzil-diallylacetal, benzil-di( ⁇ -phenylallyl)acetal, benzil-di(2-methoxyethyl)acetal, benzil-di(2-ethoxyethyl)acetal, benzil-di(2-chloroethyl)acetal, benzil-di(2-bromoethyl)acetal, benzil-di(2-chloropropyl)acetal, benzil-di(2-methylthioethyl)acetal, benzil-di(2-tert.butylthioethyl)acetal, benzil-di(2-phenylthioethyl)acetal, benzil-di(2-phenoxy
• Examples of compounds of formula Ia are: 2-phenyl-2-benzoyl-4-methyl-1,3-dioxolane, 2-phenyl-2-benzoyl-4-hexyl-1,3-dioxolane, 2-phenyl-2-benzoyl-1,3-dioxane, 2-phenyl-2-benzoyl-5-ethyl-1,3-dioxane, 2-(4-chlorophenyl)-2-(4-chlorobenzoyl)-1,3-dioxolane, and 2-(4-tolyl)-2-(4-methylbenzoyl)-1,3-dioxane.
• the cyclic monoacetals of aromatic 1,2-diketones of formula Ia can be produced by acetalisation of the corresponding benzoins, and subsequent oxidation of the benzoinacetal to benzil-monoacetal, a process described in the case of monoethyleneacetal of benzil in the Journal of Amer. Chem. Soc., 81, 633 (1959), and represented below in terms of the following formulae: ##STR6## This process is applicable also for other benzil-monoacetals of formula Ia.
• a process has now been found which enables monoacetals of aromatic 1,2-diketones of formula I to be produced, in a generally applicable manner, simply and in high yield and degree of purity.
• This process comprises the reaction of an aromatic 1,2-diketone either with a sulphurous acid ester in the presence of an anhydrous acid and of an alcohol, or with thionyl chloride and an alcohol.
• Ar 1 and Ar 2 each independently represent a phenyl radical which is unsubstituted or at most trisubstituted by halogen, alkyl or alkoxy having 1 to 4 carbon atoms or by phenyl, and this reacted with a sulphurous acid ester of the formula (R 1 CH 2 O) 2 SO in the presence of an anhydrous acid and of an alcohol of the formula R 1 CH 2 OH, or with thionyl chloride and an alcohol of the formula R 1 CH 2 OH, whereby R 1 represents hydrogen, alkyl having 1 to 5 carbon atoms, alkenyl having 2 or 3 carbon atoms, aralkyl having 7 to 9 carbon atoms, aralkenyl having 8 or 9 carbon atoms or a group --(CH 2 ) n --X wherein n denotes a whole number of 1 to 3, and X represents halogen, --
• aromatic 1,2-diketones which can be used for this process are benzil and substituted benzils such as, e.g. 4,4'-dimethylbenzil, 4,4'-diisopropylbenzil, 4,4'-diphenylbenzil, 2,2'-dimethoxybenzil, 4-methylbenzil, 3-methoxybenzil, 2,2'-dimethylbenzil, 4-chloro-4'-phenylbenzyl, 4,4'-dichlorobenzil, 3,3'-dibromobenzil, 2,4,2',4'-tetramethylbenzil, 2,4,6-trimethylbenzil, 2,4-dichloro-4'-methylbenzil.
• the production of these benzil derivatives is described in the literature; they are produced, for example, by oxidation of the corresponding benzoins.
• sulphurous acid esters which can be used for this process are dimethylsulphite, diethylsulphite, dipropylsulphite, dibutylsulphite, dihexylsulphite, diallylsulphite, di( ⁇ -phenylethyl)sulphite, di( ⁇ -phenylallyl)sulphite, di(2-chloroethyl)sulphite, di(2-methoxyethyl)sulphite, di(2-phenoxyethyl)sulphite, di(2-methylthioethyl)sulphite, di(2-phenylthioethyl)sulphite, di(2-acetoxyethyl)sulphite or di(3-carbomethoxypropyl)sulphite.
• These sulphites are produced by processes known from the literature, e.g. by reaction of the corresponding alcohols with thionyl chloride.
• the anhydrous acid employed for the purpose of accelerating the formation of acetal can be an anhydrous mineral acid such as, e.g. sulphuric acid or hydrochloric acid, or a Lewis acid such as, e.g. borofluoride or its complexes. It is preferable to use concentrated sulphuric acid, and in an amount of at least one mole per mole of diketone.
• the alcohol employed is advantageously the alcohol corresponding to the sulphurous acid ester, that is, for example, methanol with application of dimethylsulphite, or isopropanal with application of diisopropylsulphite. If the diketones are reacted with thionyl chloride and a primary monoalcohol, then as such there can be used, e.g.
• the reaction of the diketones with sulphurous acid esters in the presence of an acid and of an alcohol is generally performed at a temperature of 20° to 120° C., preferably at 40° to 100° C.
• reaction of the diketones with a mixture of thionyl chloride and alcohol is advantageously performed with cooling to ca. 02 to 20° C., whereby the sulphite forms.
• the subsequent reaction is, as described above, carried out at elevated temperature.
• a modification of the process consists in reacting a benzoin firstly with sulphuryl chloride and subsequently with thionyl chloride and an alcohol.
• a benzoin of formula III ##STR9## which is reacted with sulphuryl chloride and then with thionyl chloride and an alcohol, R 1 CH 2 OH, whereby Ar 1 , Ar 2 and R 1 have the above defined meanings.
• benzoins are, besides the unsubstituted benzoin, symmetrically or unsymmetrically substituted benzoins such as, e.g. 4-methylbenzoin, 4,4'-dimethylbenzoin, 2,2'-dimethylbenzoin, 4,4-diisopropylbenzoin, 4,4'-diphenylbenzoin, 3-methoxybenzoin, 2,2'-dimethoxybenzoin, 4,4'-dichlorobenzoin, 4-chloro-4'-phenylbenzoin, 3,3'-dibromobenzoin, 2,4,2',4'-tetramethylbenzoin, 2,4,6-trimethylbenzoin or 2,4-dichloro-4'-methylbenzoin.
• the production of these benzoins is described in the literature; in particular, they can be produced by condensation of the corresponding aromatic aldehydes.
• the procedure used is to suspend the benzoin in the sulphuryl chloride and to heat the suspension slowly to about 25°-50° C. After completion of oxidation, the excess sulphuryl chloride is distilled off and, after cooling to room temperature, the reaction with thionyl chloride and the alcohol performed as described above.
• the isolation of benzil-monoacetals from the reaction mixtures is effected by known processes: e.g. by concentration by evaporation of the solution, by the addition of water or by cooling. Yields of over 80% of crude monoacetal are obtained; as required, the resulting product can be purified by recrystallisation or distillation or by other known methods.
• the physical properties of the benzil-monoacetals are dependent to a great extent on the nature and position of the substituents; in general, the products are low-melting or oily compounds, which at room temperature are stable to an unlimited extent.
• the benzil-monoacetals producible according to the invention can be used as sensitisers for photopolymerisation of polymerisable systems containing unsaturated compounds.
• Such systems are, for example, unsaturated monomers such as acrylic acid methyl ester, -ethyl ester, -n- or tert.
• butyl ester methacrylic acid alkyl esters such as methylmethacrylate or ethylmethacrylate, di-(meth)-acrylates of aliphatic diols, acrylonitrile, methacrylonitrile, acrylamide, methacrylamide, N,N-disubstituted acrylamides and methacrylamides, vinylacetate, vinylacrylate, vinylpropionate, succinic acid divinyl ester, isobutylvinyl ether, butanediol-1,4-divinyl ether, styrene, alkylstyrene, halostyrenes, divinylbenzenes, vinylnaphthalene, N-vinyllpyrrolidone, vinyl chloride, vinylidene chloride, diallylphthalate, diallylmaleate, triallylisocyanurate, triallylphosphate, ethylene glycol diallyl ether, pentaerythrito
• Photopolymerisable systems are, in addition, unsaturated polymers and mixtures thereof with unsaturated monomers. These include, in particular, the mixtures of unsaturated polyesters with unsaturated monomers.
• unsaturated polyesters are meant, for example, polycondensation products from ⁇ , ⁇ -unsaturated dicarboxylic acids or their derivatives with polyols.
• ⁇ , ⁇ -unsaturated dicarboxylic acids or their derivatives are maleic acid, maleic acid anhydride, fumaric acid, mesaconic acid, and citraconic acid.
• unsaturated dicarboxylic acids it is also possible to incorporate, for the purpose of adjustment of the degree of unsaturation, saturated dicarboxylic acids or dicarboxylic acids inert to polymerisation.
• saturated dicarboxylic acids or dicarboxylic acids examples in this case are succinic acid, sebacic acid, isophthalic acid, phthalic acid, halogenated phthalic acids or 3,6-endomethylene- ⁇ 4 -tetrahydrophthalic acid, as well as the anhydrides of these dicarboxylic acids.
• the polyols employed for the production of polycondensation products are mainly glycols such as ethylene glycol, propanediol-1,2-diethylene glycol, 1,3-propylene glycol, 1,4-tetramethylene glycol as well as triethylene glycol.
• unsaturated polyesters are usually employed in admixture with unsaturated monomers containing allyl or vinyl groups, preferably with styrene.
• unsaturated monomers containing allyl or vinyl groups preferably with styrene.
• benzil-monoacetals of formula I or Ia can be photopolymerised in an advantageous manner to thus obtain moulding and coating compounds.
• Moulding compounds which can be photopolymerised with compounds of formula I or Ia are, for example, so-called air-drying moulding compounds. These are unsaturated polyesters containing, besides ⁇ , ⁇ -unsaturated dicarboxylic acid esters, also ⁇ , ⁇ -unsaturated ether radicals.
• Coating compounds that can be photopolymerised with compounds of formula I or Ia are, for example, lacquer coatings from unsaturated monomers and unsaturated polymers. These lacquers may also be photopolymerised by the so-called active-base process (Aktivsigvon). The coating compound is in this case applied with the photo-initiator to a peroxide-containing layer previously applied to the substrate, and subsequently photopolymerised.
• the photopolymerisable compounds or mixtures can be stabilised by addition of the usual thermal inhibitors which are employed in the production of light-sensitive compounds.
• thermal inhibitors which are employed in the production of light-sensitive compounds.
• additions can moreover be made of copper compounds such as copper naphthenate, -stearate or -octoate, phosphorus compounds such as triphenylphosphine, tributylphosphine, triethylphosphite, triphenylphosphite or tribenzylphosphate, quaternary ammonium compounds such as tetramethylammonium chloride or trimethylbenzylammonium chloride or hydroxylamine derivatives such as N,N-diethylhydroxylamine.
• the photopolymerisable compounds or mixtures can contain chain-transfer agents such as triethanolamine or cyclohexene.
• a further possibility of preventing the inhibiting action of the atmospheric oxygen is for the process to be performed under inert gas, or for fillers permeable to UV-light, such as, e.g. certain silicates, to be added to the polyester resin.
• the formulations filled in this way cure, even in air, rapidly under UV-irradiation, because the content of bonding agent is reduced at the surface.
• autoxidisable groups into the resin to be cured can eliminate the inhibiting action of the atmospheric oxygen.
• this can be effected by copolymerisation with certain allyl compounds
• the coating and moulding compounds may also contain slight amounts of the usual carriers and fillers, as well as so-called thixotropic agents, such as glass fibres, synthetic fibres, silicic acid and talcum.
• a further application of compounds of formula I is the photochemical cross-linking of polymerisates, specially of olefin polymerisates.
• olefin polymerisates are meant in this connection polyolefins such as high- and low-pressure polyethylene polypropylene, polybutylene, polyisobutylene and ethylene-vinylacetate-copolymerisates.
• copolymerisates from olefins such as ethylene, propylene, butylene or isobutylene can be cross-linked by UV-irradiation with the aid of the benzil-monoacetals.
• Benzil-monoacetals are moreover applicable for the production of photopolymerised elements from which, after irradiation and by washing-out, relief profiles for printing purposes can be produced.
• Suitable as unsaturated polymers in photopolymerisable layers for the production of relief profiles for printing purposes are, in particular, linear synthetic polyamides.
• Photopolymerisable unsaturated monomers, which are used in the mentioned polymers in light-sensitive layers for the production of relief profiles are preferably those which contain at least two polymerisable olefinic double bonds and, besides the double bonds, also amide groups such as, e.g. methylene-bis-acrylamide, methylene-bis-methacrylamide as well as bis-acryl- or bis-methacrylamides of diamines.
• a further application of the benzil-monoacetals as photosensitisers is in the drying, by UV-irradiatin, of printing pastes containing as bonding agents unsaturated monomers and unsaturated polymers. Based on bonding agents having, for example, conjugated double bonds, printing pastes which dry in a short time under the action of UV-rays can be produced.
• Such bonding agents are natural or synthetic conjuen oils, unsaturated polyester resins or polyfunctional acrylates or methacrylates.
• Such printing-paste bonding agents frequently contain as additives chain-transfer agents such as triethanolamine or cyclohexene, anti-inhibiting agents such as diallylphthalate-prepolymers, or stabilisers such as diethylhydroxylamine.
• chain-transfer agents such as triethanolamine or cyclohexene
• anti-inhibiting agents such as diallylphthalate-prepolymers
• stabilisers such as diethylhydroxylamine.
• the benzil-monoacetals according to the invention are particularly well-suited catalysts for photochemical curing.
• the benzil-monoacetals of formula I or Ia are used for the mentioned fields of application advantageously in amounts of 0.1 to 20 per cent by weight, preferably in amounts of ca. 0.5 to about 5 per cent by weight, and either singly or in admixture with each other.
• sensitisers to the photopolymerisable systems is generally effected by a simple stirring-in, since most of these systems are liquid. Usually there is obtained a solution of the sensitisers according to the invention, in consequence of which their homogeneous distribution and the transparency of the polymerisates are ensured.
• Suitable light sources for the irradiation of the substrates containing the photosensitisers of formula I or Ia are medium-pressure, high-pressure and low-pressure mercury vapour lamps, as well as superactinic fluorescent lamps, of which the emission maxima is in the range of between 300 and 400 m ⁇ .
• the precipitated potassium sulphate is removed and an amount of 2 ml of trimethylphosphite then added to the filtrate to effect separation of the residual traces of benzil; the temperature is maintained for 2 hours at room temperature, the filtrate then concentrated by evaporation to dryness and the residue distilled in vacuo.
• Benzildimethylacetal distills at 140°-141°/0.5 mm in the form of a colourless oil, which crystallises in the receiver; M.P. 62°-63°.
• Benzildimethylacetal is obtained by this process in a yield of 85-90% of theory, calculated on the amount of benzil used.
• a crystalline precipitate forms as the solution cools.
• An addition is made dropwise at between 7° and 10° of 350 ml of water, and the reaction mixture stirred.
• the crystalline precipitate is filtered off under suction, washed with isopropanol/water 1:1 and dried at 40° in vacuo.
• Benzildimethylacetal is obtained by this process in the form of white crystals in a yield of 84% of theory.
• a suspension of 21.0 g of benzil in 23.8 g of thionylchloride is cooled to 0°, and 35.3 g of 2-chloroethanol added dropwise to the suspension at between 0° and 5° in the course of 30 minutes.
• the reaction mixture is stirred for 6 hours at room temperature and subsequently for 1 hour at 50°-60°; it is then concentrated in a rotary evaporator, and 3 g of potassium carbonate and 0.6 ml of trimethylphosphite are added to the residue; the whole is afterwards taken up in 40 ml of isopropanol. Water is added and a crystalline precipitate formed. This is filtered off under suction and recrystallised from isopropanol to obtain benzil-di- ⁇ -chloroethyl-acetal in the form of white crystals, M.P. 58°-59°.
• the irradiated solution is cooled in order to prevent a thermal polymerisation.
• the solution of the formed polymerisate in the monomer is rinsed with small amounts of ethylacetate in a round flask, and the solvent and the unpolymerised monomeric fraction are subsequently distilled off in a rotary evaporator.
• the polymeric residue is dried in a vacuum drying chamber at 50°-60° and afterwards weighed.
• the amount of polymerisation is below 0.1%.
• a 2% solution of known photosensitisers and of photosensitisers according to the invention in unsaturated polyester resin is prepared at 25°, and in each case the flow-through-time of a specific amount of the particular solution through a graduated buret determined.
• the solution is then stored in the dark at room temperature and, after 2, 4 and 8 weeks' storage time, the flow-through-time determined in the same manner. Polyester resin containing no additive is taken as a comparison. The results of these tests are given in Table 4:
• Benzildimethylacetal in a concentration of 0.5% is worked, on mixing rolls, into polyethylene of density 0.92. From the rolled sheet obtained are pressed films 0.1 mm in thickness, which are irradiated for 40 minutes with a high-pressure mercury vapour lamp at a distance of 10 cm. The irradiated film specimens are then extracted in boiling toluene for 5 hours. The extraction residue, which corresponds to the cross-linked proportion of the polyethylene, amounts to 24% of the weight of the film used. Without photosensitiser, but otherwise under the same conditions as those described above, no extraction residue remains.

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